Power plant condensers are devices that bring about a reduction in the counterpressure by condensing the exhaust steam of steam turbines. Their task is to dissipate to the outside the thermal energy of the steam that has not been converted into electricity.
Familiar devices are, for instance, surface condensers, which consist of a housing with a built-in network of pipes. During operation of the power plant, turbine steam flows through an inlet, through the condenser neck, and into the condensation chamber, where it is condensed on the outside of the condensate pipes, through which a coolant, usually cooling water, flows. The condensate that is formed is then collected in a condensate collector, the so-called hot well, in the lower part of the condenser and subsequently returned to the steam circulation system by means of condensate pumps. In this process, it passes through the preheater and the feed-water line, reaching the boiler, where it is evaporated once again and drives the turbines as working steam.
Via the turbine counterpressure, the capacity of the condenser decisively influences the efficiency of the entire installation and thus the power of the generator.
Since the condenser pressure is below atmospheric pressure, some leakage air is continuously penetrating the condenser. This air as well as other non-condensable fractions such as, for example, endogenous non-condensable radiolysis gases (non-condensable mixture of H2 and O2 from the stoichiometric breakdown of water) have to be removed from the condensers.
For this purpose, deaerating or degassing suction apparatuses are used that are connected to the condensers in such a way that, at a place with the lowest possible vapor pressure and with the highest possible gas concentration, they suction off a gas-steam mixture from the condensation chamber of the condensers.
The reason for this measure is the worsening of the condensation capacity and thus of the condensation pressure in power plants caused by the reduction in the heat-transfer coefficient due to the presence of even small concentrations of non-condensable components, which are also referred to as inert gases.
This worsening is already noticeable at a fraction of a percentage in the mole fraction and, from about 1% onwards (mole fraction of air=0.01), it causes a drastic worsening of the heat transfer. In order to minimize this effect, so-called air coolers are installed in the condensation chamber.
Air coolers are funnel-shaped sheet metal structures in the piping system. They cause a spatial acceleration of the steam-inert gas mixture, so that the steam speed at the pipe web does not drop too low due to the self-suctioning effect of the condensation and of the suction system, thus remaining within the range of 2 to 3 m/s. This partially reduces the negative effect of the non-condensable gases. At the end of the funnel-shaped air cooler, the gas-steam mixture, which has an inert-gas fraction ranging from a few percent to about 20% in the mole fraction (mole fraction of air=0.2), is then discharged to the outside by means of the suction aggregates, for instance, vacuum pumps. Furthermore, the concentration of the inert gases in the mixture causes a significant reduction in the mass-volume flow of the mixture to be suctioned off.
Therefore, the air cooler arranged inside the condenser has the function of attaining the greatest possible concentration of the inert gases (non-condensable gases) in the mixture since this is to bring about the following advantages:                improvement of the capacity of the vacuum pumps (low suction pressure);        reduction in the requisite vacuum pump capacity;        reduction in the loss of circulation material (pure water).        
If the concentration of the non-condensable components is too low, the suction apparatus is additionally thermally stressed due to the enthalpy load caused by the excess steam, as a result of which cavitation problems occur when liquid-seal pumps and water-jet aspirators are employed, whereas steam-jet ejectors are less susceptible to this phenomenon.
The loss of condensation capacity due to the presence of inert gases is drastic. For instance, the condensation capacity typically amounts to 20 to 30 kW/m2 in the main condensation pipe system and it can drop to 0.3 to 0.5 kW/m2 in the preheater and air-cooler chamber. This corresponds to a reduction of the rates of heat flow per unit of area by one and a half orders of magnitude.
The drawback of this known state of the art is that there is often insufficient suction capacity in the power plants, especially when the condensers of boiling water reactors undergo retrofitting along with a concurrent increase in output. In such cases, the available suction capacity is usually no longer sufficient for the newly established pressure and for the current thermal output.
But the occurrence of problems due to insufficient suction capacity is also encountered in conventional and nuclear plants with pressurized water reactors. The reason for this lies, for example, in inadequate bundled designs, perforations and leaks in the lines as well as in an improvement of the vacuum due to retrofits since the existing suction apparatuses are not dimensioned for this.
Another disadvantage of the known state of the art is, for instance, the pressure loss via the suction line.